Phase.4　To further technological advancement

Fujikura outruns counterparts in the U.S. with wires having a length of 100m and leads the world in IcL value, the product of critical current and length.

In 2004, Fujikura was preparing to produce the world's first 100-m-long superconducting wires with a critical current of more than 100 A. The year fell on the opening year of the biennial Applied Superconductivity Conference. As many superconductivity researchers were to take part in the Conference, we planned to present the result of 100-m-long superconducting wires in the Conference and started the preparations in July. To produce the superconducting wires, we had to deposit films on the intermediate layer, superconducting layer, and stabilizing layer, and then treat them with heat. As the film deposition equipment in those days was smaller and had less power than now, it was taking us more than 2 months to complete a sequence of the processes.

Just then, when we completed an intermediate layer and then were trying to deposit a film of the superconducting layer on top of it, an important part of the excimer laser that we used broke down. We inquired at the manufacturer's agents and other research organizations regarding parts of the same type, but we did not find a replacement. When all seemed to be over for us, the idea that we could manage to produce 100-m-long superconducting wires with an excimer laser that we used for basic experiments came to us in a flash. We, however, would have to not only move the position of the excimer laser, but also repipe the laser material gas and coolant water if we had followed the method. We had only a few 10-hour periods that we could spend for the construction work, considering the presentation day in the Conference. Fujikura's engineering corps immediately started measuring the site and pipes on the spot and then started the construction work the next morning. We prepared the research paper that would be presented in the Conference, up to the point where we would only have to fill in the characteristic values, obtained the characteristics of the superconducting wires two days before the presentation, and managed to present the paper in the Conference successfully.

In those days, the U.S. had just started a project with an aim to develop 100-m-long superconducting wires four years later, when researchers in the U.S. heard a report from Japan that a company had achieved the target in Japan. It was said that they could not believe what they were hearing. "Unbelievable" was the word used to express the situation. It was easy to imagine that the accomplishment might cause jealousy and resentment among them.

200-m-long Superconducting WireSix months after the development of the 100-m-long superconducting wires with a critical current of 100 A, Fujikura focused on the development of 200-m-long superconducting wires with a critical current of 200 A. We faced many difficulties, but we broke through every one of them. We finally brought them to reality in fiscal year 2006. The NEDO project planned to develop 500-m-long superconducting wires with a critical current of 300 A by the end of fiscal year 2007. This was why Fujikura entered the trial and error process for developing a longer superconducting layer. In the summer of 2007, we tackled the first production of the superconducting wires, and we established a basic technology for producing the long superconducting wires as a result. The continuous length reached 368 m and its critical current exceeded 300 A, and the minimum critical current was 305 A among the values. In fact, the IcL value (the product of critical current and length) of the time was 112,000 Am. We led the world in this field, although it only lasted for a short period of four months. After that, we made every possible effort to enhance the superconducting layer production process to improve the superconducting characteristics, and finally completed 500-m-long superconducting wires through the film deposition of an intermediate layer. We achieved a critical current value of 350 A for the whole length of 504 m. The IcL value of the time was 176,000 Am, which meant that we had again won the world's number one position in this field.

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  500-m-long Superconducting Wire

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  Characteristic of 500-m-long Superconducting Wire